Method for determining precoding matrix indicator, user equipment, and base station evolved NodeB

ABSTRACT

The present disclosure relates to a method for determining a precoding matrix indicator, a user equipment (UE), a base station (e.g., eNB), and a system. The method includes: receiving a reference signal sent by a base station; selecting, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of two matrices W 1  and W 2 , where W 1  is a block diagonal matrix, where each block matrix is a Kronecker product of a matrix A i  and a matrix B i ; and sending a precoding matrix indicator (PMI) to the base station, where the PMI corresponds to the selected precoding matrix, so that the base station obtains the precoding matrix according to the PMI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/164,719, filed on Oct. 18, 2018, which is a continuation of U.S.application Ser. No. 15/834,984 filed on Dec. 7, 2017, now U.S. Pat. No.10,122,427, which is a continuation of U.S. application Ser. No.14/923,019 filed on Oct. 26, 2015, now U.S. Pat. No. 9,859,962, which isa continuation of U.S. application Ser. No. 14/569,522 filed on Dec. 12,2014 now U.S. Pat. No. 9,203,491, which is a continuation ofInternational Application No. PCT/CN2012/076898, filed on Jun. 14, 2012.All of the afore-mentioned patent applications are hereby incorporatedby reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of mobile communications, andin particular, to a method for determining a precoding matrix indicator,a user equipment, a base station evolved NodeB, and a system.

BACKGROUND

A multiple-input multiple-output (MIMO) radio system can obtaindiversity and array gains by means of transmit precoding and receivesignal combination. A system that utilizes precoding may be expressedas:y=H{circumflex over (V)}s+n

where y represents a vector of a received signal, H represents a channelmatrix, {circumflex over (V)} represents a precoding matrix, srepresents a vector of a transmitted symbol, and H represents ameasurement noise.

Optimal precoding generally requires that channel state information(CSI) is completely known by a transmitter. A commonly used method isthat a user equipment (UE) or a mobile station (MS) (hereinaftergenerally referred to as UE) quantizes instantaneous CSI and feeds backthe CSI to a NodeB, which includes a base station (BS), an access point,a transmission point (TP), or an evolved NodeB (eNB), where the evolvedNodeB is generally referred to as an eNB. CSI information that is fedback by an existing Long Term Evolution (LTE) R8 system includesinformation such as a rank indicator (RI), a precoding matrix indicator(PMI), and a channel quality indicator (CQI), where the RI and the PMIrespectively indicate the number of layers used and a precoding matrix.A set of used precoding matrices is generally referred to as a codebook,where each precoding matrix is a codeword in the codebook. To reducesystem costs and meet higher requirements on the system capacity andcoverage, an active antenna system (AAS) is already widely deployed inpractice. Compared with an existing base station antenna, the AASfurther provides a degree of freedom in design for the verticaldirection.

An existing 4-antenna codebook, which is designed based on Householdertransformation, of an LTE R8 system and an existing 8-antenna codebook,which is designed based on dual codebooks, of an LTE R10 system aremainly designed for a horizontal antenna, but a degree of freedom of avertical antenna is not considered. When the 4-antenna codebook and the8-antenna codebook are directly used in deployment of an AAS basestation antenna, system performance severely deteriorates.

SUMMARY

Embodiments of the present invention provide a method for determining aprecoding matrix indicator, a user equipment, a base station evolvedNodeB eNB, and a system, which use a precoding matrix that supportsvertical and horizontal quantization, and can fully use a degree offreedom of an active antenna system in a vertical direction, therebyimproving CSI feedback accuracy and system throughput.

According to one aspect, an embodiment of the present invention providesa method for determining a precoding matrix indicator, where the methodincludes:

receiving a reference signal sent by a base station;

selecting, based on the reference signal, a precoding matrix from acodebook, where a precoding matrix W included in the codebook is aproduct of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B)}, where each block matrix X_(i) is a Kronecker product of a matrixA_(i) and a matrix B_(i), that is X_(i)=A_(i)⊗B_(i) and 1≤i≤N_(B); andthe W₁ includes at least one block matrix, that is, the number of blockmatrices is N_(B)≥1; and

sending a precoding matrix indicator PMI to the base station, where thePMI corresponds to the selected precoding matrix, so that the basestation obtains the precoding matrix according to the PMI.

According to another aspect, an embodiment of the present inventionfurther provides a method for determining a precoding matrix indicator,where the method includes:

sending a reference signal to a user equipment UE; and

receiving a precoding matrix indicator PMI sent by the UE, where the PMIcorresponds to a precoding matrix that is selected by the U, based onthe reference signal, from a codebook; and a precoding matrix W includedin the codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B)}, where each block matrix X_(i) is a Kronecker product of a matrixA_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); andthe matrix W₁ includes at least one block matrix, that is, the number ofblock matrices is N_(B)≥1.

According to another aspect, correspondingly, an embodiment of thepresent invention provides a user equipment UE, including:

a receiving unit, configured to receive a reference signal sent by abase station;

a selecting unit, configured to select, based on the reference signal, aprecoding matrix from a codebook, where a precoding matrix W included inthe codebook is a product of two matrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B)}, where each block matrix X_(i) is a Kronecker product of a matrixA_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); andthe W₁ includes at least one block matrix, that is, the number of blockmatrices is N_(B)≥1; and

a sending unit, configured to send a precoding matrix indicator PMI tothe base station, where the PMI corresponds to the selected precodingmatrix, so that the base station obtains the precoding matrix accordingto the PMI.

According to another aspect, correspondingly, an embodiment of thepresent invention provides a base station eNB, including:

a sending unit, configured to send a reference signal to a userequipment UE; and

a receiving unit, configured to receive a precoding matrix indicator PMIsent by the UE, where the PMI corresponds to a precoding matrix that isselected by the UE, based on the reference signal, from a codebook; anda precoding matrix W included in the codebook is a product of twomatrices W₁ and W₂, where

W₁ is a block diagonal matrix, that is, W₁=diag{X₁, . . . , X_(N) _(B)}, where each block matrix X_(i) is a Kronecker product of a matrixA_(i) and a matrix B_(i), that is, X_(i)=A_(i)⊗B_(i), and 1≤i≤N_(B); andthe matrix W₁ includes at least one block matrix, that is, the number ofblock matrices is N_(B)≥1.

According to another aspect, correspondingly, an embodiment of thepresent invention further provides a system for determining a precodingmatrix indicator, including the foregoing terminal UE and base stationeNB.

The method for determining a precoding matrix indicator, the userequipment UE, the base station eNB, and the system according to theembodiments of the present invention utilize a precoding matrix thatsupports vertical and horizontal quantization, which can not only use adegree of freedom in a horizontal direction, but also can use a degreeof freedom in a vertical direction, thereby greatly improving CSIfeedback accuracy and system throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a first embodiment of a method for determininga precoding matrix indicator according to the present invention;

FIG. 2 is a flowchart of a second embodiment of a method for determininga precoding matrix indicator according to the present invention;

FIG. 3 is a schematic structural diagram of composition of a system fordetermining a precoding matrix indicator according to the presentinvention;

FIG. 4 is a schematic structural diagram of composition of a userequipment UE in FIG. 3 ; and

FIG. 5 is a schematic structural diagram of composition of a basestation eNB in FIG. 3 .

DETAILED DESCRIPTION

The following further describes the technical solutions of the presentinvention in detail with reference to the accompanying drawings andembodiments.

According to embodiments of the present invention, a codebook scheme isdesigned for an actual network deployment and antenna configuration, andespecially for a base station antenna configuration condition of anactive antenna system. According to the codebook scheme, a UE selectsand reports a PMI, and a NodeB performs precoding according to PMIinformation reported by the UE, so as to improve performance of a systemwith the foregoing antenna configuration and especially with the AASbase station antenna configuration. The base station antenna can notonly use a degree of freedom in a horizontal direction, but also can usea degree of freedom in a vertical direction.

FIG. 1 is a flowchart of a first embodiment of a method for determininga precoding matrix indicator according to the present invention. Asshown in the figure, this embodiment specifically includes the followingsteps:

Step 101: Receive a reference signal sent by a base station.

Specifically, the reference signal sent by the base station may includea channel state information reference signal (CSI RS), a demodulationreference signal (demodulation RS, DM RS), or a cell-specific referencesignal (cell-specific RS, CRS). A user equipment UE may obtain aresource configuration of the reference signal by receiving anotification (for example, RRC (Radio Resource Control) signaling ordownlink control information DCI) from an eNB or based on a cellidentity ID, and obtain the reference signal from a correspondingresource or subframe.

Step 102: Select, based on the reference signal, a precoding matrix froma codebook, where a precoding matrix W included in the codebook is aproduct of two matrices W₁ and W₂, that is:W=W ₁ W ₂  (1)

where W₁ is a block diagonal matrix, that is:W ₁=diag{X ₁ . . . ,X _(N) _(B) }  (2)

where each block matrix X_(i) is a Kronecker product of a matrix A_(i)and a matrix B_(i), that is:X _(i) =A _(i) ⊗B _(i),1≤i≤N _(B)  (3)

the W₁ includes at least one block matrix, that is, the number N_(B) ofblock matrices is:N _(B)≥1  (4)

Specifically, each column of the matrix A_(i) or of the matrix B_(i) informula (3) may be a discrete Fourier transform (DFT) vector or may be acolumn vector of a Hadamard matrix, that is:A _(i)=[a ₀ a ₁ . . . a _(N) _(a) ⁻¹]  (5)B _(i)=[b ₀ b ₁ . . . b _(N) _(b) ⁻¹]  (6)therefore:a _(k) ∈{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ },k=0, . . . ,N _(a)−1  (7)ora _(k) ∈{h ₀ ,h ₁ , . . . ,h _(N) _(h) ⁻¹ },k=0, . . . ,N _(a)−1  (8)orb _(l) ∈{f ₀ ,f ₁ , . . . ,f _(N) _(f) ⁻¹ },l=0, . . . ,N _(b)−1  (9)orb _(l) ∈{h ₀ ,h ₁ , . . . ,h _(N) _(h) ⁻¹ },l=0, . . . ,N _(b)−1  (10)

where N_(a) and N_(b) represent the numbers of columns of the matrixA_(i) and the matrix B_(i), respectively; h_(m), m=0, . . . , N_(h)−1represents a column vector of the Hadamard matrix, where N_(h)represents the number of columns of the Hadamard matrix; and f_(n)=0, .. . , N_(f)−1 represents a DFT vector, where N_(f) is the number of DFTvectors, and the DFT vector f_(n) may be represented as:

$\begin{matrix}{f_{n} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot n}}{N}}e^{j\frac{2{\pi \cdot 1 \cdot n}}{N}}\cdots e^{j\frac{2{\pi \cdot {({M - 1})} \cdot n}}{N}}} \right\rbrack^{T}} & (11)\end{matrix}$

where both M and N are integers.

Specifically, the matrix A_(i) or the matrix B_(i) in formula (3) mayalso be a precoding matrix in a 2-antenna codebook or a 4-antennacodebook of an LTE R8 system, or in an 8-antenna codebook of an LTE R10system.

Further, the matrix W₂ is used to select or weight and combine a columnvector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be:A _(i) =a ₀ ,i=1,2  (12)where:a ₀ ∈{f ₀ ,f ₁ , . . . ,f ₃}  (13)[f ₀ ,f ₁ ,f ₂ ,f ₃]=diag{1,e ^(jnπ/8) ,e ^(jnπ/4) ,e ^(jnπ/8) }F ₄,n=0,1,2,3  (14)

$\begin{matrix}{{F_{4} = {\frac{1}{2} \times \begin{bmatrix}1 & 1 & 1 & 1 \\1 & j & {- 1} & {- j} \\1 & {- 1} & 1 & {- 1} \\1 & {- j} & {- 1} & j\end{bmatrix}}}{or}} & (15)\end{matrix}$ $\begin{matrix}{{a_{k} \in \left\{ {h_{0},h_{1},\ldots,h_{3}} \right\}},{k = 0},\ldots,3} & (16)\end{matrix}$ $\begin{matrix}{\left\lbrack {h_{0},h_{1},\ldots,h_{3}} \right\rbrack = {\frac{1}{2} \times H_{4}}} & (17)\end{matrix}$

where H₄ is a Hadamard matrix of order 4.

$\begin{matrix}{{B_{i} \in \left\{ {{{\left\lbrack {b_{{({2k})}{mod}32}b_{{({{2k} + 1})}{mod}32}b_{{({{2k} + 2})}{mod}32}b_{{({{2k} + 3})}{mod}32}} \right\rbrack:k} = 0},1,\cdots,15} \right\}},{i = 1},2} & (18)\end{matrix}$ $\begin{matrix}{{b_{{({{2k} + l})}{mod}32} = \left\lbrack {e^{j\frac{2{\pi \cdot 0 \cdot {({{({{2k} + l})}{mod}32})}}}{32}}e^{j\frac{2{\pi \cdot 1 \cdot {({{({{2k} + l})}{mod}32})}}}{32}}e^{j\frac{2{\pi \cdot 2 \cdot {({{2k} + l})}}{mod}32}{32}}e^{j\frac{2{\pi \cdot 3 \cdot {({{({{2k} + l})}{mod}32})}}}{32}}} \right\rbrack^{T}},{l = 0},1,2,3} & (19)\end{matrix}$

where x mod y represents an operation of x mod y; and j represents aunit pure imaginary number, that is, j=√{square root over (−1)}; or

B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of an LTE R8system.

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}} & (20)\end{matrix}$ $\begin{matrix}{{Y \in \left\{ {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{4}} \right\}}{or}} & (21)\end{matrix}$ $\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}} & (22)\end{matrix}$ $\begin{matrix}{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} \right),\left( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} \right),\left( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} \right)} \right\}} & (23)\end{matrix}$

where {tilde over (e)}_(n), n=1, 2, 3, 4 represents a 4×1 selectionvector in which all elements are 0 except the n^(th) element being 1.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayalso separately be:A _(i)=[a ₀ a _(l)],i=1,2  (24)a ₀ ,a ₁ ∈{f ₀ ,f ₁ , . . . f ₃}  (25)

where f_(i), i=0, . . . , 3 is shown in formula (14).

ora ₀ ,a ₁ ∈{h ₀ ,h ₁ , . . . ,h ₃}  (26)

where h_(i), i=0, . . . , 3 is shown in formula (17);

the matrix B_(i), i=1, 2 is shown in formulas (18) and (19), or thematrix B_(i) is a precoding matrix in a 4-antenna rank-4 codebook of anLTE R8 system;

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \right\}} & (27)\end{matrix}$ $\begin{matrix}{Y \in {\left\{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6},e_{7},e_{8}} \right\}{or}}} & (28)\end{matrix}$ $\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}} & (29)\end{matrix}$ $\begin{matrix}{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)} \right\}} & (30)\end{matrix}$

where e_(n), n=1, 2, . . . , 8 represents an 8×1 selection vector inwhich all elements are 0 except the n^(th) element being 1.

Specifically, the selecting, based on the reference signal, a precodingmatrix from a codebook includes:

obtaining, by the user equipment UE based on the reference signal, achannel estimate; and selecting, based on a predefined criterion such asa channel capacity or throughput maximization criterion, the precodingmatrix from the codebook according to the channel estimate. Selecting,based on a predefined criterion, a precoding matrix is an existingtechnology, and details are not described herein.

Further, the selecting, based on the reference signal, a precodingmatrix from a codebook includes:

selecting, based on the reference signal, the precoding matrix from acodebook subset, where

the codebook subset may be a codebook subset that is predefined; or acodebook subset that is reported by the UE to the base station eNB,determined by the base station eNB based on the report from the UE, andnotified to the UE; or a codebook subset that is determined and reportedby the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include:

a subset of the matrix W₁, the matrix A_(i), the matrix B_(i), or thematrix W₂.

The selecting, based on the codebook subset, the precoding matrix canfurther reduce feedback overheads and implementation complexity.

Further, the codebook subsets have a same subset of the matrix W₁ thematrix A_(i), the matrix B_(i), or the matrix W₂. In this way, thecodebook subsets overlap each other, which can overcome an edge effectof channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈jmay be unequal, or may also be equal. If there are multiple cases thatX_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j thatare equal may appear in pairs, the feedback overheads can be furtherreduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also useanother form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further bemultiplied by a scale factor, so as to implement power normalization orpower equalization.

Step 103: Send a precoding matrix indicator PMI to the base station,where the PMI corresponds to the selected precoding matrix, so that thebase station obtains the precoding matrix according to the PMI.

Specifically, the precoding matrix is included in a precoding matrix setor a codebook; and the PMI is used to indicate the selected precodingmatrix in the precoding matrix set or the codebook.

Specifically, sending a precoding matrix indicator PMI to the basestation includes: sending the precoding matrix indicator PMI to the basestation, where the PMI may include only one specific value. In thiscase, the PMI directly indicates the precoding matrix W. For example, ifthere are a total of 16 different precoding matrices, PMI=0, . . . , 15may be used to respectively indicate precoding matrices W whose labelsare 0, 1, . . . , 15.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI₁ andPMI₂ to the base station, where PMI₁ and PMI₂ are used to indicate thematrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) in formula (2) and the matrix W₂,respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B)and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in thecodebook; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the basestation, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrixA_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂,respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrixB_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁,PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precodingmatrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domaingranularities or frequency domain granularities, for example, PMI₁ andPMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods orbandwidth channel features, or are obtained based on different subframeperiods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂are sent to the base station according to different time periods.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI_(1,i),1≤i≤N_(B); and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B) andPMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) andthe matrix W₂, respectively; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i) and PMI₂ tothe base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used toindicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), andthe matrix W₂, respectively.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI_(1,i),1≤i≤N_(B)/2 and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B)/2and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i),1≤i≤N_(B)/2 and the matrix W₂, respectively; and in this case,X_(2i−1)=X_(2i), and the matrices appear in pairs; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ tothe base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used toindicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2 the matrixB_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and inthis case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear inpairs.

Specifically, sending a precoding matrix indicator PMI to the basestation may be sending, by the U, the precoding matrix indicator PMI tothe base station through a physical uplink control channel (PUCCH) or aphysical uplink shared channel (PUSCH).

Further, sending a precoding matrix indicator PMI to the base stationmay be separately sending, by the UE by using different subframes oraccording to different periods, the foregoing PMI₁ and PMI₂; or PMI₁₁,PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i),PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; orPMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

Further, sending a precoding matrix indicator PMI to the base stationmay also be separately sending, by the UE for different subbands orsubband sizes in a frequency domain, the foregoing PMI₁ and PMI₂; orPMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; orPMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2,and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the basestation.

In this embodiment of the present invention, a user equipment determinesand sends a precoding matrix indicator PMI, where the PMI indicates aprecoding matrix. The precoding matrix has a structure of W=W₁W₂, whereW₁ is a block diagonal matrix in which each block matrix on a diagonalline is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrixA_(i) or the matrix B_(i) effectively supports channel state informationquantization in a horizontal direction or a vertical direction,respectively. This can fully use a degree of freedom of an activeantenna system AAS in a horizontal direction and a vertical direction,thereby greatly improving channel state information feedback accuracy.In addition, multiple block matrices X_(i) may separately correspond toantenna groups of different polarizations or at different locations, sothat the foregoing precoding matrix matches multiple antenna deploymentsor configurations. The foregoing codebook structure greatly improvesperformance of MIMO, and especially that of MU-MIMO. Moreover, one ormore PMIs are fed back based on a subset to indicate a precoding matrix,which fully uses time/frequency domain/spatial correlation of a channel,thereby greatly reducing feedback overheads.

FIG. 2 is a flowchart of a second embodiment of a method for determininga precoding matrix indicator according to the present invention. Asshown in the figure, this embodiment specifically includes:

Step 201: Send a reference signal to a user equipment U.

Specifically, the reference signal may include a channel stateinformation reference signal (CSI RS), a demodulation reference signal(demodulation RS, DM RS), or a cell-specific reference signal(cell-specific RS, CRS). Abase station eNB may notify the user equipmentUE of a resource configuration of the reference signal by using RRC(Radio Resource Control) signaling or downlink control information DCI),and instruct the UE to obtain the reference signal from a correspondingresource or subframe. The user equipment UE may also implicitly obtain,based on other information such as a cell identity ID, the resourceconfiguration of the reference signal, and obtain the reference signalfrom the corresponding resource or subframe.

Step 202: Receive a precoding matrix indicator PMI sent by the userequipment UE, where the PMI corresponds to a precoding matrix selectedby the user equipment, based on the reference signal, from a codebook;and a precoding matrix W included in the codebook is a product of twomatrices W₁ and W₂, and the precoding matrix has a structure shown informulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) maybe a DFT vector or is a column vector of a Hadamard matrix, as shown informulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be aprecoding matrix in a 2-antenna codebook or a 4-antenna codebook of anLTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a columnvector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (12) to (23); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (24) to (30); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, selecting, based on the reference signal, a precodingmatrix from a codebook includes:

selecting, based on the reference signal, the precoding matrix from acodebook subset, where

the codebook subset may be a codebook subset that is predefined; or acodebook subset that is reported by the UE to the base station eNB,determined by the base station eNB based on the report from the UE, andnotified to the UE; or a codebook subset that is determined and reportedby the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁, thematrix A_(i), the matrix B_(i), or the matrix W₂.

Further, the codebook subsets have a same subset of the matrix W₁, thematrix A_(i), the matrix B_(i), or the matrix W₂. In this way, thecodebook subsets overlap each other, which can overcome an edge effectof channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈jmay be unequal, or may also be equal. If there are multiple cases thatX_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j thatare equal may appear in pairs, feedback overheads can be furtherreduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also useanother form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further bemultiplied by a scale factor, so as to implement power normalization orpower equalization.

Specifically, the precoding matrix is included in a precoding matrix setor a codebook; and the PMI is used to indicate the selected precodingmatrix in the precoding matrix set or the codebook.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE includes: receiving the precoding matrix indicator PMIsent by the user equipment UL, where the PMI may include only onespecific value. In this case, the PMI directly indicates the precodingmatrix W. For example, if there are a total of 16 different precodingmatrices, PMI=0, . . . , 15 may be used to respectively indicateprecoding matrices W whose labels are 0, 1 . . . 15.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may also include: receiving precoding matrixindicators PMI₁ and PMI₂ sent by the user equipment UE, where PMI₁ andPMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), informula (2) and the matrix W₂, respectively; and in this case, thematrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), and the matrix W₂ are respectivelyindicated by PMI₁ and PMI₂ in the codebook; or

receiving precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ sent by theuser equipment UE, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate thematrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂,respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrixB_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁,PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precodingmatrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domaingranularities or frequency domain granularities, for example, PMI₁ andPMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods orbandwidth channel features, or are obtained based on different subframeperiods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂are sent to the base station according to different time periods.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may also include: receiving precoding matrixindicators PMI_(1,i), 1≤i≤N_(B), and PMI₂ sent by the user equipment UE,where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrixX_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), and the matrix W₂, respectively; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i),1≤i≤N_(B), and the matrix W₂ respectively; or

receiving precoding matrix indicators PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂sent by the user equipment UE, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ areused to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N/2, andthe matrix W₂ respectively; and in this case, X_(2i−1)=X_(2i), and thematrices appear in pairs; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂sent by the user equipment UE, where PMI₁₁, PMI_(12,i), and PMI₂ areused to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrixB_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and inthis case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear inpairs.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may be receiving, through a physical uplink controlchannel (PUCCI) or a physical uplink shared channel (PUSCH), theprecoding matrix indicator PMI sent by the user equipment UE.

Further, receiving a precoding matrix indicator PMI sent by the userequipment UE may be separately receiving, by the base station by usingdifferent subframes or according to different periods, the foregoingPMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) andPMI₂ or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i),PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂ that are sent by the user equipmentUE; or

may also be receiving the foregoing PMI₁ and PMI₂; or PMI₁₁, PMI₁₂, andPMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂; or PMI_(11,i), PMI_(12,i),1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂that are sent for different subbands or subband sizes in a frequencydomain by the user equipment U.

In this embodiment of the present invention, a base station eNB receivesa precoding matrix indicator PMI sent by a user equipment UE, where thePMI indicates a precoding matrix. The precoding matrix has a structureof W=W₁W₂, where W₁ is a block diagonal matrix in which each blockmatrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B),where the matrix A_(i) or the matrix B_(i) effectively supports channelstate information quantization in a horizontal direction or a verticaldirection, respectively. This can fully use a degree of freedom of anactive antenna system AAS in a horizontal direction and a verticaldirection, thereby greatly improving channel state information feedbackaccuracy. In addition, multiple block matrices X_(i) may separatelycorrespond to antenna groups of different polarizations or at differentlocations, so that the foregoing precoding matrix matches multipleantenna deployments or configurations. The foregoing codebook structuregreatly improves performance of MIMO, and especially that of MU-MIMO.Moreover, one or more PMIs are fed back based on a subset to indicate aprecoding matrix, which fully uses time/frequency domain/spatialcorrelation of a channel, thereby greatly reducing feedback overheads.

The following describes a system for determining a precoding matrixindicator, a user equipment UE, and a base station eNB in the presentinvention in detail.

FIG. 3 is a schematic structural diagram of composition of an embodimentof a system for determining a precoding matrix indicator according tothe present invention. The system according to this embodiment of thepresent invention includes a user equipment UE 11 and a base station eNB12. For a structure of the user equipment UE 11, refer to FIG. 4 ; andfor a schematic structural diagram of the base station eNB 12, refer toFIG. 5 .

FIG. 4 is a schematic diagram of a user equipment UE 11 for determininga precoding matrix indicator according to an embodiment of the presentinvention. As shown in the figure, the user equipment UE 11 includes: areceiving unit 111, a selecting unit 112, and a sending unit 113.

The receiving unit 111 is configured to receive a reference signal sentby a base station.

Specifically, the reference signal sent by the base station may includea channel state information reference signal (CSI RS), a demodulationreference signal (demodulation RS, DM RS), or a cell-specific referencesignal (cell-specific RS, CRS). The user equipment UE may obtain aresource configuration of the reference signal by receiving anotification (for example, RRC (Radio Resource Control) signaling ordownlink control information DCI) from an eNB or based on a cellidentity ID, and obtain the reference signal from a correspondingresource or subframe.

The selecting unit 112 is configured to select, based on the referencesignal, a precoding matrix from a codebook, where a precoding matrix Wincluded in the codebook is a product of two matrices W₁ and W₂; and theprecoding matrix has the structure shown in formulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) maybe a DFT vector or may be a column vector of a Hadamard matrix, as shownin formulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be aprecoding matrix in a 2-antenna codebook or a 4-antenna codebook of anLTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a columnvector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (12) to (23); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is A=2 and there are32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (24) to (30); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, selecting, based on the reference signal, a precodingmatrix from a codebook includes:

obtaining, by the user equipment UE based on the reference signal, achannel estimate and selecting, based on a predefined criterion such asa channel capacity or throughput maximization criterion, the precodingmatrix from the codebook according to the channel estimate. Selecting,based on a predefined criterion, a precoding matrix is an existingtechnology, and details are not described herein.

Further, selecting, based on the reference signal, a precoding matrixfrom a codebook includes:

selecting, based on the reference signal, the precoding matrix from acodebook subset, where

the codebook subset may be a codebook subset that is predefined; or acodebook subset that is reported by the UE to the base station eNB,determined by the base station eNB based on the report from the UE, andnotified to the UE; or a codebook subset that is determined and reportedby the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁ thematrix A_(i), the matrix B_(i), or the matrix W₂.

Selecting, based on the codebook subset, the precoding matrix canfurther reduce feedback overheads and implementation complexity.

Further, the codebook subsets have a same subset of the matrix W₁, thematrix A_(i), the matrix B_(i), or the matrix W₂. In this way, thecodebook subsets overlap each other, which can overcome an edge effectof channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈jmay be unequal, or may also be equal. If there are multiple cases thatX_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j thatare equal may appear in pairs, the feedback overheads can be furtherreduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also useanother form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further bemultiplied by a scale factor, so as to implement power normalization orpower balancing.

The sending unit 113 is configured to send a precoding matrix indicatorPMI to the base station, where the PMI corresponds to the selectedprecoding matrix, so that the base station obtains the precoding matrixaccording to the PMI.

Specifically, the precoding matrix is included in a precoding matrix setor a codebook; and the PMI is used to indicate the selected precodingmatrix in the precoding matrix set or the codebook.

Specifically, sending a precoding matrix indicator PMI to the basestation includes: sending the precoding matrix indicator PMI to the basestation, where the PMI may include only one specific value. In thiscase, the PMI directly indicates the precoding matrix W. For example, ifthere are a total of 16 different precoding matrices, PMI=0, . . . , 15may be used to respectively indicate precoding matrices W whose labelsare 0, 1, . . . , 15.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI₁ andPMI₂ to the base station, where PMI₁ and PMI₂ are used to indicate thematrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) in formula (2) and the matrix W₂,respectively; and in this case, the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B),and the matrix W₂ are respectively indicated by PMI₁ and PMI₂ in thecodebook; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the basestation, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate the matrixA_(i), 1≤i N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂,respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrixB_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁,PMI₁₂, and PMI₂ in the codebook.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI_(1,i)1≤i≤N_(B)/2 and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B)/2and PMI₂ are used to indicate a matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i),1≤i≤N_(B)/2 and the matrix W₂ respectively; and in this case,X_(2i−1)=X_(2i), and the matrices appear in pairs; or

sending precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂ tothe base station, where PMI_(11,i), PMI_(12,i), and PMI₂ are used toindicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrixB_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and inthis case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear inpairs.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precodingmatrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domaingranularities or frequency domain granularities, for example, PMI₁ andPMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods orbandwidth channel features, or are obtained based on different subframeperiods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂are sent to the base station according to different time periods.

Specifically, sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI_(1,i),1≤i≤N_(B) and PMI₂ to the base station, where PMI_(1,i), 1≤i≤N_(B) andPMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) andthe matrix W₂, respectively; or

sending precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ to the basestation, where PMI_(11,i), PMI_(12,i), and PMI₂ are used to indicate thematrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂,respectively.

Specifically, sending a precoding matrix indicator PMI to the basestation may be sending, by the UE, the precoding matrix indicator PMI tothe base station through a physical uplink control channel (PUCCH) or aphysical uplink shared channel (PUSCH).

Further, sending a precoding matrix indicator PMI to the base stationmay be separately sending, by the UL by using different subframes oraccording to different periods, the foregoing PMI₁ and PMI₂; or PMI₁₁,PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i),PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂; orPMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the base station.

Further, sending a precoding matrix indicator PMI to the base stationmay also be separately sending, by the UE for different subbands orsubband sizes in a frequency domain, the foregoing PMI₁ and PMI₂; orPMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B), and PMI₂; orPMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(1,i), 1≤i≤N_(B)/2,and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2 and PMI₂ to the basestation.

In this embodiment of the present invention, a user equipment determinesand sends a precoding matrix indicator PMI, where the PMI indicates aprecoding matrix. The precoding matrix has a structure of W=W₁W₂, whereW₁ is a block diagonal matrix in which each block matrix on a diagonalline is X_(i)=A_(i)⊗B_(i), and i=1, . . . , N_(B), where the matrixA_(i) or the matrix B_(i) effectively supports channel state informationquantization in a horizontal direction or a vertical direction,respectively. This can fully use a degree of freedom of an activeantenna system AAS in a horizontal direction and a vertical direction,thereby greatly improving channel state information feedback accuracy.In addition, multiple block matrices X_(i) may separately correspond toantenna groups of different polarizations or at different locations, sothat the foregoing precoding matrix matches multiple antenna deploymentsor configurations. The foregoing codebook structure greatly improvesperformance of MIMO, and especially that of MU-MIMTO. Moreover, one ormore PMIs are fed back based on a subset to indicate a precoding matrix,which fully uses time/frequency domain/spatial correlation of a channel,thereby greatly reducing feedback overheads.

FIG. 5 is a base station eNB 12 for determining a precoding matrixindicator according to an embodiment of the present invention. As shownin the figure, the base station eNB 12 includes: a sending unit 121 anda receiving unit 122.

The sending unit 121 is configured to send a reference signal to a userequipment UE.

Specifically, the reference signal may include a channel stateinformation reference signal (CSI RS), a demodulation reference signal(demodulation RS, DM RS), or a cell-specific reference signal(cell-specific RS, CRS). Abase station eNB may notify the user equipmentUE of a resource configuration of the reference signal by using RRC(Radio Resource Control) signaling or downlink control information (DC),and instruct the UE to obtain the reference signal from a correspondingresource or subframe. The user equipment UE may also implicitly obtain,based on other information such as a cell identity ID, the resourceconfiguration of the reference signal, and obtain the reference signalfrom the corresponding resource or subframe. The receiving unit 122 isconfigured to receive a precoding matrix indicator PMI sent by the userequipment UE, where the PMI corresponds to a precoding matrix selected,based on the reference signal, from a codebook by the user equipment;and a precoding matrix W included in the codebook is a product of twomatrices W₁ and W₂, and the precoding matrix W has the structure shownin formulas (1) to (4).

Specifically, each column of the matrix A_(i) or of the matrix B_(i) maybe a DFT vector or may be a column vector of a Hadamard matrix, as shownin formulas (5) to (11); or

specifically, the matrix A_(i) or the matrix B_(i) may also be aprecoding matrix in a 2-antenna codebook or a 4-antenna codebook of anLTE R8 system, or in an 8-antenna codebook of an LTE R10 system.

Further, the matrix W₂ is used to select or weight and combine a columnvector in the matrix W₁, so as to form the matrix W.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (12) to (23); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

In an example in which the number of block matrices is N_(B)=2 and thereare 32 transmit antennas, matrices that form the precoding matrix W mayseparately be those shown in formulas (24) to (30); or B_(i) is aprecoding matrix in a 4-antenna rank-4 codebook of an LTE R8 system.

Specifically, the precoding matrix selected, based on the referencesignal, from a codebook includes: the precoding matrix selected, basedon the reference signal, from a codebook subset, where

the codebook subset may be a codebook subset that is predefined; or acodebook subset that is reported by the UE to the base station eNB,determined by the base station eNB based on the report from the UE, andnotified to the UE; or a codebook subset that is determined and reportedby the UE, for example, a latest reported codebook subset.

Further, the codebook subset may include a subset of the matrix W₁, thematrix A_(i), the matrix B_(i), or the matrix W₂.

Further, the codebook subsets have a same subset of the matrix W₁, thematrix A_(i), the matrix B_(i), or the matrix W₂. In this way, thecodebook subsets overlap each other, which can overcome an edge effectof channel state information quantization.

Further, in the precoding matrix, block matrices X_(i) and X_(j), i≈jmay be unequal, or may also be equal. If there are multiple cases thatX_(i) and X_(j), i≈j are equal, for example, X_(i) and X_(j), i≈j thatare equal may appear in pairs, feedback overheads can be furtherreduced.

In addition, the foregoing matrix A_(i) or matrix B_(i) may also useanother form, which is not further elaborated herein.

It should be noted that, each of the foregoing matrices may further bemultiplied by a scale factor, so as to implement power normalization orpower balancing.

Specifically, the precoding matrix is included in a precoding matrix setor a codebook; and the PMI is used to indicate the selected precodingmatrix in the precoding matrix set or the codebook.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE includes: receiving the precoding matrix indicator PMIsent by the user equipment UE, where the PMI may include only onespecific value. In this case, the PMI directly indicates the precodingmatrix W. For example, if there are a total of 16 different precodingmatrices, PMI=0, . . . , 15 may be used to respectively indicateprecoding matrices W whose labels are 0, 1, . . . 15.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may also include: receiving precoding matrixindicators PMI₁ and PMI₂ sent by the user equipment UE, where PMI₁ andPMI₂ are used to indicate the matrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) informula (2) and the matrix W₂, respectively; and in this case, thematrix X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) and the matrix W₂ are respectivelyindicated by PMI₁ and PMI₂ in the codebook; or

receiving precoding matrix indicators PMI₁₁, PMI₁₂, and PMI₂ sent by theuser equipment UE, where PMI₁₁, PMI₁₂, and PMI₂ are used to indicate thematrix A_(i), 1≤i≤N_(B), the matrix B_(i), 1≤i≤N_(B), and the matrix W₂,respectively; and in this case, the matrix A_(i), 1≤i≤N_(B), the matrixB_(i), 1≤i≤N_(B), and the matrix W₂ are respectively indicated by PMI₁₁,PMI₁₂, and PMI₂ in the codebook.

Further, the precoding matrix indicators PMI₁ and PMI₂, or the precodingmatrix indicators PMI₁₁, PMI₁₂, and PMI₂ have different time domaingranularities or frequency domain granularities, for example, PMI₁ andPMI₂, or PMI₁₁, PMI₁₂, and PMI₂ separately indicate different periods orbandwidth channel features, or are obtained based on different subframeperiods or subband sizes.

Alternatively, further, the precoding matrix indicators PMI₁₁ and PMI₁₂are sent to the base station according to different time periods.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may also include: receiving precoding matrixindicators PMI_(1,i), 1≤i≤N_(B), and PMI₂ sent by the user equipment UE,where PMI_(1,i), 1≤i≤N_(B) and PMI₂ are used to indicate the matrixX_(i)=A_(i)⊗B_(i), 1≤i≤N_(B) the matrix W₂, respectively; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂are used to indicate the matrix A_(i), 1≤i≤N_(B), the matrix B_(i),1≤i≤N_(B), and the matrix W₂, respectively; or receiving precodingmatrix indicators PMI_(1,i), 1≤i≤N_(B)/2, and PMI₂ sent by the userequipment UE, where PMI_(1,i), 1≤i≤N_(B)/2 and PMI₂ are used to indicatea matrix X_(2i−1)=X_(2i)=A_(2i)⊗B_(2i), 1≤i≤N_(B)/2, and the matrix W₂,respectively; and in this case, X_(2i−1)=X_(2i), and the matrices appearin pairs; or

receiving precoding matrix indicators PMI_(11,i), PMI_(12,i), and PMI₂sent by the user equipment UE, where PMI_(11,i), PMI_(12,i), and PMI₂are used to indicate a matrix A_(2i−1)=A_(2i), 1≤i≤N_(B)/2, the matrixB_(2i−1)=B_(2i), 1≤i≤N_(B)/2, and the matrix W₂, respectively; and inthis case, A_(2i−1)=A_(2i), B_(2i−1)=B_(2i), and the matrices appear inpairs.

Specifically, receiving a precoding matrix indicator PMI sent by theuser equipment UE may be receiving, through a physical uplink controlchannel (PUCCI) or a physical uplink shared channel (PUSCH), theprecoding matrix indicator PMI sent by the user equipment UE.

Further, receiving a precoding matrix indicator PMI sent by the userequipment UE may be separately receiving, by the base station by usingdifferent subframes or according to different periods, the foregoingprecoding matrix indicators sent by the user equipment UE, which arePMI₁ and PMI₂; or PMI₁₁, PMI₁₂, and PMI₂; or PMI_(1,i), 1≤i≤N_(B) andPMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B), and PMI₂; or PMI_(11,i),PMI_(12,i), 1≤i≤N_(B)/2, and PMI₂; or

may also be receiving the foregoing PMI₁ and PMI₂; or PMI₁₁ PMI₁₂, andPMI₂; or PMI_(1,i), 1≤i≤N_(B) and PMI₂; or PMI_(11,i), PMI_(12,i),1≤i≤N_(B), and PMI₂; or PMI_(11,i), PMI_(12,i), 1≤i≤N_(B)/2, and PMIthat are sent for different subbands or subband sizes in a frequencydomain by the user equipment UE.

In this embodiment of the present invention, the base station eNBreceives a precoding matrix indicator PMI sent by the user equipment UE,where the PMI indicates a precoding matrix. The precoding matrix has astructure of W=W₁W₂, where W₁ is a block diagonal matrix in which eachblock matrix on a diagonal line is X_(i)=A_(i)⊗B_(i), and i=1, . . . ,N_(B), where the matrix A_(i) or the matrix B_(i) effectively supportschannel state information quantization in a horizontal direction or avertical direction, respectively. This can fully use a degree of freedomof an active antenna system AAS in a horizontal direction and a verticaldirection, thereby greatly improving CSI feedback accuracy. In addition,multiple block matrices X_(i) may separately correspond to antennagroups of different polarizations or at different locations, so that theforegoing precoding matrix matches multiple antenna deployments orconfigurations. The foregoing codebook structure greatly improvesperformance of MIMO, and especially that of MU-MIMO. Moreover, one ormore PMIs are fed back based on a subset to indicate a precoding matrix,which fully uses time/frequency domain/spatial correlation of a channel,thereby greatly reducing feedback overheads.

A person skilled in the art may be further aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware, computer software, or a combination thereof. Toclearly describe the interchangeability between the hardware and thesoftware, the foregoing has generally described structures and steps ofeach example according to functions. Whether the functions are performedby hardware or software depends on particular applications and designconstraint conditions of the technical solutions. A person skilled inthe art may use different methods to implement the described functionsfor each particular application, but it should not be considered thatthe implementation goes beyond the scope of the present invention.

In combination with the embodiments disclosed in this specification,method or algorithm steps may be implemented by hardware, a softwaremodule executed by a processor, or a combination thereof. The softwaremodule may reside in a random access memory (RAM), memory, a read-onlymemory (ROM), an electrically programmable ROM, an electrically erasableprogrammable ROM, a register, a hard disk, a removable disk, a CD-ROM,or any other form of storage medium known in the art.

The foregoing specific embodiments further describe the objectives,technical solutions, and beneficial effects of the present invention indetail. It should be understood that the foregoing descriptions aremerely specific embodiments of the present invention, but are notintended to limit the protection scope of the present invention. Anymodification, equivalent replacement, or improvement made withoutdeparting from the spirit and principle of the present invention shouldfall within the protection scope of the present invention.

What is claimed is:
 1. A method for determining a precoding matrixindicator, the method comprising: sending, by a base station, areference signal to a terminal device; and receiving, by the basestation, a precoding matrix indicator (PMI) from the terminal device,wherein the PMI corresponds to a precoding matrix in a codebook, whereineach precoding matrix W comprised in the codebook is a product of twomatrices W₁ and W₂, W=W₁W₂, wherein the matrix W₁ is a block diagonalmatrix, W₁=diag{X₁, . . . , X_(N) _(B) }, N_(B)>1, each block matrixX_(i) being a Kronecker product of a matrix A_(i) and a matrix B_(i),X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrixB_(i) are for channel state information quantization in two degrees offreedom of an antenna array respectively.
 2. The method according toclaim 1, wherein each column of the matrix A_(i) and the matrix B_(i) isa discrete Fourier transform (DFT) vector, and the two degrees offreedom of the antenna array comprise a degree of freedom in ahorizontal direction and a degree of freedom in a vertical direction. 3.The method according to claim 1, wherein receiving by the base stationthe PMI from the terminal device comprises: receiving a third precodingmatrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and afifth precoding matrix indicator PMI₂ from the terminal device, whereinthe third precoding matrix indicator PMI₁₁ is used to indicate thematrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicatorPMI₁₂ is used to indicate the matrix B_(i), wherein 1≤i≤N_(B), and thefifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.4. The method according to claim 1, wherein block matrices in the matrixW₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 5. The method according toclaim 1, wherein the matrix W₂ is used to select or weight and combineat least one column vector in the matrix W₁ to form the matrix W.
 6. Themethod according to claim 1, wherein the codebook comprises a codebooksubset consisting of precoding matrices corresponding to a subset of thematrix A_(i) and the matrix B_(i).
 7. The method according to claim 6,further comprises: notifying, by the base station, the subset of thematrix A_(i) and the matrix B_(i) to the terminal device.
 8. A device,comprising: a transmitter configured to send a reference signal to aterminal device; and a receiver configured to receive a precoding matrixindicator (PMI) from the terminal device, wherein the PMI corresponds toa precoding matrix in a codebook, wherein each precoding matrix Wcomprised in the codebook is a product of two matrices W₁ and W₂,W=W₁W₂, wherein the matrix W₁ is a block diagonal matrix, W₁=diag{X₁, .. . , X_(N) _(B) }, N_(B)>1, each block matrix X_(i) being a Kroneckerproduct of a matrix A_(i) and a matrix B_(i), X_(i)=A_(i) ⊗B_(i),1≤i≤N_(B), wherein the matrix A_(i) and the matrix B_(i) are for channelstate information quantization in two degrees of freedom of an antennaarray respectively.
 9. The device according to claim 8, wherein eachcolumn of the matrix A_(i) and the matrix B_(i) is a discrete Fouriertransform (DFT) vector, and the two degrees of freedom of the antennaarray comprise a degree of freedom in a horizontal direction and adegree of freedom in a vertical direction.
 10. The device according toclaim 8, wherein receiving the PMI from the terminal device comprises:receiving a third precoding matrix indicator PMI₁₁, a fourth precodingmatrix indicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ fromthe terminal device, wherein the third precoding matrix indicator PMI₁₁is used to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourthprecoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i),wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is usedto indicate the matrix W₂.
 11. The device according to claim 8, whereinblock matrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.12. The device according to claim 8, wherein the matrix W₂ is used toselect or weight and combine at least one column vector in the matrix W₁to form the matrix W.
 13. The device according to claim 8 wherein thecodebook comprises a codebook subset consisting of precoding matricescorresponding to a subset of the matrix A_(i) and the matrix B_(i). 14.The device according to claim 13, the transmitter is configured tonotify the subset of the matrix A_(i) and the matrix B_(i) to theterminal device.
 15. A non-transitory computer-readable storage mediumstoring instructions which, when executed by at least one processor in abase station, cause the base station to: send a reference signal to aterminal device; and receive a precoding matrix indicator (PMI) from theterminal device, wherein the PMI corresponds to a precoding matrix in acodebook, wherein each precoding matrix W comprised in the codebook is aproduct of two matrices W₁ and W₂, W=W₁W₂, wherein the matrix W₁ is ablock diagonal matrix, W₁=diag {X₁, . . . , X_(N) _(B) }, N_(B)>1, eachblock matrix X_(i) being a Kronecker product of a matrix A_(i) and amatrix B_(i), X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) andthe matrix B_(i) are for channel state information quantization in twodegrees of freedom of an antenna array respectively.
 16. Thenon-transitory computer-readable storage medium according to claim 15,wherein each column of the matrix A_(i) and the matrix B_(i) is adiscrete Fourier transform (DFT) vector, and the two degrees of freedomof the antenna array comprise a degree of freedom in a horizontaldirection and a degree of freedom in a vertical direction.
 17. Thenon-transitory computer-readable storage medium according to claim 15,wherein receiving the PMI from the terminal device comprises: receivinga third precoding matrix indicator PMI₁₁, a fourth precoding matrixindicator PMI₁₂, and a fifth precoding matrix indicator PMI₂ from theterminal device, wherein the third precoding matrix indicator PMI₁₁ isused to indicate the matrix A_(i), wherein 1≤i≤N_(B); the fourthprecoding matrix indicator PMI₁₂ is used to indicate the matrix B_(i)wherein 1≤i≤N_(B), and the fifth precoding matrix indicator PMI₂ is usedto indicate the matrix W₂.
 18. The non-transitory computer-readablestorage medium according to claim 15, wherein block matrices in thematrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 19. The non-transitorycomputer-readable storage medium according to claim 15, wherein thematrix W₂ is used to select or weight and combine at least one columnvector in the matrix W₁ to form the matrix W.
 20. The non-transitorycomputer-readable storage medium according to claim 15, wherein thecodebook comprises a codebook subset consisting of precoding matricescorresponding to a subset of the matrix A_(i) and the matrix B_(i). 21.The non-transitory computer-readable storage medium according to claim20, wherein the instructions which, when executed by at least oneprocessor in the base station, cause the base station to notify thesubset of the matrix A_(i) and the matrix B_(i) to the terminal device.22. A communications device, comprising: at least one processor; and amemory configured to store computer operation instructions that, whenexecuted by the at least one processor, cause the at least one processorto perform: sending a reference signal to a terminal device; andreceiving a precoding matrix indicator (PMI) from the terminal device,wherein the PMI corresponds to a precoding matrix in a codebook, whereineach precoding matrix W comprised in the codebook is a product of twomatrices W₁ and W₂, W=W₁W₂, wherein the matrix W₁ is a block diagonalmatrix, W₁=diag{X₁, . . . , X_(N) _(B) }N_(B)>1 each block matrix X_(i)being a Kronecker product of a matrix A_(i) and a matrix B_(i),X_(i)=A_(i)⊗B_(i), 1≤i≤N_(B), wherein the matrix A_(i) and the matrixB_(i) are for channel state information quantization in two degrees offreedom of an antenna array respectively.
 23. The communications deviceaccording to claim 22, wherein each column of the matrix A_(i) and thematrix B_(i) is a discrete Fourier transform (DFT) vector, and the twodegrees of freedom of the antenna array comprise a degree of freedom ina horizontal direction and a degree of freedom in a vertical direction.24. The communications device according to claim 22, wherein receivingthe PMI from the terminal device comprises: receiving a third precodingmatrix indicator PMI₁₁, a fourth precoding matrix indicator PMI₁₂, and afifth precoding matrix indicator PMI₂ from the terminal device, whereinthe third precoding matrix indicator PMI₁₁ is used to indicate thematrix A_(i), wherein 1≤i≤N_(B); the fourth precoding matrix indicatorPMI₁₂ is used to indicate the matrix B_(i) wherein 1≤i≤N_(B), and thefifth precoding matrix indicator PMI₂ is used to indicate the matrix W₂.25. The communications device according to claim 22, wherein blockmatrices in the matrix W₁ satisfy X_(2j−1)=X_(2j), 1≤j≤N_(B)/2.
 26. Thecommunications device according to claim 22, wherein the matrix W₂ isused to select or weight and combine at least one column vector in thematrix W₁ to form the matrix W.
 27. The communications device accordingto claim 22, wherein the codebook comprises a codebook subset consistingof precoding matrices corresponding to a subset of the matrix A_(i) andthe matrix B_(i).
 28. The communications device according to claim 27,the at least one processor is further caused to perform: notifying thesubset of the matrix A_(i) and the matrix B_(i) to the terminal device.